First go to /forum where you of course are if you are reading this topic. Then go to "Index" scrolling down until you see this:

These are all of the clans of our server as of 6th of January, 2017! Let's say you want to join [BLS] and you clicked on their section and by clicking on it, you'll reach here: In the image above, the topic which I am pointing at is "[BLS] Clan's Requirements & Format" topic (it's exterior). By clicking on it and you'll reach here: (This is its interior) Here you can see the requirements and format. If you meet the requirements, just copy the format and go to their section's home here in this picture ([BLS] one): And apply there (This was an example, you can join any clan you want like this, because maximum steps are the same). Keep in mind, it may take a while for the application to be processed. You will be required to log into the game in order for you to enter the actual clan, since the adding members command does not work offline.

Note: ALMOST every clan has a requirements and format topic in their section, and as per the maximum clan rules, you have to post your application in their homepage, but not in each one of them because it can be that their section's moderators has set a different page for you guys to apply.

NOTE: Not every clan has requirements or an application, as some are private and require other means of joining.